Famous astrophysicist Neil deGrasse Tyson answered an interesting question after a lecture he gave on Thursday in Denver. When Tyson was asked why the human race has never had contact yet with an alien species, he replied as follows.

“[Enrico Fermi] said that the universe has been around a really long time, and technological evolution, when it happens, happens fast. If there are aliens in the galaxy, they should have been here by now. Because if they live approximately as long as we do, they can send colonies out to other star systems, set up base camps, and then send out other colonies. So one grows to ten, grows to a hundred, grows to a thousand. And you can grow the number of colonies exponentially in the world very quickly, so where are they?”

Neil, widely known for having a decent sense of humor, gave one humorous reason to start with.

“[The aliens may have] already visited, but they happened to land during Comic-Con, and nobody noticed them.”

The acclaimed astrophysicist then got serious.

“Another hypothesis is that if you are of a culture that wants to colonize another planet, another star system, that says something about you. You’re not happy with just one planet, you want more. So you go, and you claim this new planet. This keeps going, but if everybody who’s doing that has that mentality, you reach the point where you start running out of planets. And then what happens? War.”

“It may be that the very urge to colonize star systems is the force that prevents it from colonizing the entire galaxy — because they put themselves out of business,” deGrasse Tyson explained. He said that acquiring all that new real estate is inconsistent with what is in reality required to create a “harmonious systems of colonized planets.”

Several theories as to why we haven’t met aliens yet have been put forth by human scientists in the past. The Rare Earth Theory says basically that “Earth is special,” in that the chain of events that led to life on our planet is so complex that despite the size of the universe, there may not be that much sentient life out there to get in contact with. Still other scientists say that we may have been contacted via some sort of communication technique that we don’t yet understand. Though our earthly satellite dishes and radio telescopes are trained on the skies, we may not be seeing — or understanding — what a distant civilization is transmitting. Still others think the universe is just too darn big. The Earth may lie in what effectively might be the “backwoods” territory of the universe — (think of us as residing in the Outer Rim, Star Wars fans) — and we’re just too removed to be on anyone’s proverbial radar. Still other scientists think that aliens might regard us as uninteresting; an advanced species capable of moving freely through the stars might look upon us as we would look at a small cluster of bugs on the side of a tree, and it’s only our human ego that makes us think we’re actually worth visiting.

Neil deGrasse Tyson wrapped up his answer of the question with a third possibility of why we haven’t met any aliens as of yet.

“I’m all in for this one, is that we have been visited — on days other than when Comic-Con was in progress — but they looked around and concluded that there was no intelligent life on Earth and left forever.”

What do you think? Why haven’t we been visited by aliens yet — or have we?